The invention relates to a disc brake for a commercial vehicle having a brake caliper designed as a sliding caliper and a brake disc, in which caliper a brake pad is arranged on a clamping side and on a reaction side, which upon a brake application by a brake application device can be pressed against the brake disc on both sides. The brake pad on the reaction side supports itself with a pad backing plate carrying a friction pad on a rear-end wall of the caliper. The invention also relates to a corresponding brake pad for a disc brake.
Such disc brakes are primarily employed with commercial vehicles. On actuating a brake application device, a brake pad on the clamping side and subsequently a brake pad on the reaction side are pressed against the brake disc for braking. The brake pads are usually positioned in pad shafts of a fixed-location caliper mount, wherein during a brake application their backing plates bear against horns of the caliper mount in the circumferential direction of the brake disc, through which the forces that occur during braking or the braking moment acting on the brake pads are absorbed.
Clamping of the brake, i.e. the bearing of the brake pads against the brake disc on both sides, during which the clamping force is active in the axial direction of the brake disc, leads to a loading of the brake caliper and, in the case of a suitably high braking force, to its deformation such that the brake caliper expands in the axial direction on its side facing the brake disc axis. Because of this, the region of the rear-end wall of the brake caliper located opposite and forming a bearing surface against the pad backing plate facing an assembly opening for inserting the brake pads is more strongly pressed against the pad backing plate. This means that the pressure distribution of the pad backing plate on the reaction side is variable.
Over the lifespan of the brake pad on the reaction side, the uneven bearing pressure leads to a high wear, the so-called radial tilted wear of the friction pad in the region facing the assembly opening.
Thus, a certain wear limit is already reached in this region while the friction pad material in the remaining regions is still adequate in its thickness. The brake pad therefore has to be replaced at an early stage, which obviously does not allow for a service life as long as possible.
To rectify this, it is proposed in DE 29 25 785 A1, to form a gap, in a non-functioning position, that is wider relative to the adjoining region between the rear-end wall of the brake caliper and the reaction-end brake pad in a region facing an assembly opening of the brake caliper. This is created in that the pad backing plate on its back facing the rear-end wall of the brake caliper is bevelled towards the assembly opening.
However, this results in substantial production engineering problems during the manufacture of the brake pad. Here, the friction pad material is usually applied onto the pad backing plate by pressing with high pressures and increased temperatures. In the process, the pad backing plate is supported with its back on a plane-flat thrust bearing of a press tool. A necessary support for absorbing the pressing pressure in the plumb direction is not ensured through the incline of the back, with the consequence that the friction pad is not applied sufficiently homogeneously. This leads to a reduction of the service life of the friction pad and, under certain conditions, to a restriction of the operational safety of the brake pad as a whole.
In addition to this, a high wear of the expensive press tool through lateral forces that occur through the reduced support of the pad backing plate has to be additionally complained about.
On the whole, this brake pad thus does not satisfy the demands made for an optimized service life and a maximum cost-effective production.
The invention is based on the object of further developing a disc brake of the generic type and a brake pad for a disc brake so that their service life is optimized and the operational safety improved.
This and other objects are achieved by providing a disc brake, and corresponding brake pad, having a brake caliper designed as a sliding caliper and a brake disc, in which caliper a brake pad is arranged on a clamping side and on a reaction side, which upon a brake application by a brake application device can be pressed against the brake disc on both sides. The brake pad on the reaction side supports itself with a pad backing plate, which carries a friction pad, on a rear-end wall of the caliper. Between the rear-end wall of the caliper and the reaction-side brake pad a gap is formed in a region facing an assembly opening of the caliper in a non-operational position. The gap is wider in the region facing the assembly opening relative to the adjoining region. A length of the gap corresponds at least to the length of the bearing of the wall on the pad backing plate in an operational or contact pressure position. The gap is formed by providing at least one recess in the back of the pad backing plate. The back of the pad backing plate is parallel and otherwise planar relative to the side carrying the friction pad. The recess runs spaced from the edges of the pad backing plate delimiting the longitudinal sides.
Through the invention it is achieved that the brake-induced wear of the brake pad on the reaction side takes place evenly, as a result of which a longer service life is obtained.
Here, the deformation of the brake caliper in the sense described can be accepted. In fact, an even lighter embodiment of the brake caliper is possible, since for this purpose merely the larger gap that is provided in the unbraked position of the disc brake, according to the invention between the rear-end wall of the brake caliper and the brake pad on the reaction side, has to be suitably adjusted, i.e. widened in a region facing the assembly opening of the brake caliper relative to the adjoining region.
The lighter design of the brake caliper that is possible through the invention fits in well with an always demanded weight optimization of the disc brake. In particular, this results in that the fuel consumption is reduced and thus the operating costs are lowered without influencing the functional safety. In addition, the production costs are also favorably influenced through the material reduction in the design of the new brake caliper.
In addition to this, the invention offers the advantage that a deformation of the brake disc in the axial direction created through braking heat known as “coning” is not critical insofar as the brake pad can now evade the largest expansion of the brake disc during “coning” in the region of the assembly opening. Thus, the pressure distribution between the friction pad and the brake disc is improved and the crack sensitivity of the brake disc that has been complained about up to now, reduced.
Depending on the clamping force and thus deformation degree of the brake caliper, the rear-end wall of the brake caliper increasingly comes to bear against the pad backing plate of the brake pad, wherein the surface pressure, which results from the exerted force and the bearing area between the rear-end wall of the brake caliper and of the pad backing plate, substantially remains the same throughout the entire clamping.
The wider gap according to the invention is achieved through a recess, the dimensioning of which is determined by the deformation behaviour of the brake caliper and which runs spaced from the edges of the pad backing plate delimiting the long sides.
Since the back with the recess located opposite the friction pad as a whole runs parallel to the side carrying the friction pad, a full-surface support of the pad backing plate in the press tool is obtained during the manufacture of the brake pad, which is positioned exactly transversely to the pressing direction.
At least the two edge regions of the back of the pad backing plate assigned to the long sides of the pad backing plate are plane-flat and thus form a full support.
The recess can be designed so that the adjoining plane-flat regions are large in area, which guarantees a good heat transfer and an even force introduction.
This, in turn, is prerequisite in order to achieve a homogeneous strength of the friction pad, as is required on the one hand for a service life optimization and on the other hand for a high operational safety.
In addition to this, the wear of the press tool is reduced through the even force distribution during pressing, with the result that the invention to a quite remarkable extent leads to a reduction of the production and operating costs.
Usually, the brake pads in their contour correspond to the brake disc, i.e. they are formed in the sense of a circular ring segment. The contour of the recess corresponds to that of the bearing surface of the wall and extends almost over the entire length of the pad backing plate or is segmented corresponding to the design and the deformation behavior of the brake caliper. Here, the recess can run symmetrically or asymmetrically to the radial axis.
Depending on requirement, the recess in the pad backing plate can be designed in a sharp-edged manner or with flat transitions to the adjoining regions that are raised relative to the recess, wherein the angles of the transitions are adapted to the deformations that are expected during the operation. The depth of the recess is dependent on the production possibility, however in particular on the strength of the pad backing plate and is preferably between 0.5 and 2 mm.
In addition to a production of the recess through a cutting process, the recess can also be produced through a shaping method, for example through stamping or the like. It is also contemplated to produce the recess through eroding or to introduce it during the forming of the pad backing plate as casting during the casting operation.
Contrary to this unitary formation of the pad backing plate, the recess can also be provided by way of an insert that can be joined into the pad backing plate.
In any case there is a possibility of subsequently inserting the new brake pad into an existing brake caliper, for example as part of a replacement, so that the advantages of the invention materialize also with existing brake systems.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.